Hi,
Both Delta and Alaska used to allow VHF scanners in flight.
The url below from the Internet Wayback Machine shows the old Delta page which explicitly referenced them:
http://web.archive.org/web/200008180...nics/index.jsp
The reference is removed on the current corresponding page on delta-air.com
Regretfully I do not have a URL from Alaska but If you do a google search of the newsgroup rec.radio.scanners you can find extensive threads on this topic.
I do not recall that scanners were ever explicitly allowed on United.
Steve (u600213)
[This message has been edited by u600213 (edited 02-23-2003).]